This invention is concerned generally with paper cutting machines, and more specifically paper cutting machines with dual knife pulldown rods driven by dual gearboxes. The invention automates the process of obtaining proper positioning of a paper cutting knife after a knife change.
On large paper cutting machines with cutting knives often three feet, four feet or wider, the cutting knife must be replaced with a sharpened knife after several thousand cuts, typically about 3,000 to 3,500 cuts. Typically the knife rides on a moving beam that descends toward the paper at an oblique angle (often about 45°) and which changes in orientation relative to the paper-supporting surface as it descends, from slightly non-parallel to parallel. The paper is pinched between the sharpened end of the knife and a “cutting stick” which is at the surface carrying the paper. The blade edge impinges only slightly into the surface of the cutting stick.
On the change of a paper cutting knife, the replacement knife will have a slightly different depth, i.e. height from top to bottom. The movement of the knife-holding beam is governed by pull arms near left and right ends of the beam, and both pull arm mechanisms must be adjusted to place the replacement blade edge at precisely the right height so that it cuts the paper properly, engaging properly against the cutting stick below during each cut.
Typically the operator uses a computer, a graphical user interface including a monitor, during the knife change. The user sets the system for a knife change and sends the knife down to the cutting stick. The knife-cutting beam will stop automatically at the bottom. The user removes two knife bolts at one side of the knife, then returns the beam and knife to the top position. At that point the cutting stick may be turned over or around for a new edge. The operator removes the remaining knife bolts, and again lowers the knife. He then removes the dull knife and places the sharp knife for lifting onto the beam. He can use a bolt key (used also to remove the bolts) to lift the sharp knife so that the bolts can be replaced. Once all bolts are loosely fitted, the operator tightens the center bolt.
From here, the operator has to more or less manually adjust the top position of the knife and bottom position of the knife, via the beam top and bottom positions and using the left and right pull arm mechanisms. This includes, after installing the new knife, raising the beam to the high point and then adjusting turnbuckles on the pull arms to set the knife at a position that will be somewhat high when the knife is lowered, then lowering the beam/knife and adjusting one side of the beam (e.g. the right side) to put the adjacent knife edge at a precise height relative to the cutting stick. Then the operator adjusts the opposite-side pull arm via its turnbuckle until the knife edge at that end engages the cutting stick precisely as desired. A test cut can then be made.
The adjustments of the pull arm turnbuckles in the typical conventional system required the operator to use wrenches for rotation of the turnbuckle nuts. The procedure for knife exchange tended to be time consuming and inconvenient for operators.